I Saw on every ic's datasheet or any circuit board there is a max power rateing showed as +-52 , +-48 etc. My question is when a circuit required max -+50 vdc and we use a ac transformer like 25-0-25 in a bridge rectifiers and capacitors the DC final voltage show 1.41 times means about -+70.5 voltage. So that means I'm crossing the max limit of the circuit?
Datasheets always show the absolute maximum and often also recommended maximum voltages. These are always DC values.
A 25-0-25 volt transformer would generate plus 35 volts and minus 35 volts (so 70 volts in total)
If a circuit specifies -/+ 50 volts maximum then that is assumed to be a DC value (unless specifically stated otherwise such as the input to a power supply board) and so we work back and say that 50 volts DC needs 50/1.414 which is 35 volts AC. So we would need a 35-0-35 transformer.
A 25-0-25 volt transformer would generate plus 35 volts and minus 35 volts (so 70 volts in total)
If a circuit specifies -/+ 50 volts maximum then that is assumed to be a DC value (unless specifically stated otherwise such as the input to a power supply board) and so we work back and say that 50 volts DC needs 50/1.414 which is 35 volts AC. So we would need a 35-0-35 transformer.
+- 50V DC means two supply rails, at +50V and -50V together with a 0V rail.
A 25-0-25 AC secondary will give you something +35VDC, 0V, and -35V DC - if used with the usual bipolar PSU arrangements. 35V is less than 50V, so all is well.
A 25-0-25 AC secondary will give you something +35VDC, 0V, and -35V DC - if used with the usual bipolar PSU arrangements. 35V is less than 50V, so all is well.
Thank you for your reply. @Mooly so as you say, I got a stk4231 ic and over on the circuit board and data sheet says Vcc Max +/- 75. So I can use a AC Transformer like 50-50?? I want to use the max power to generate the max output power from the I'm.
> use the max power to generate the max output power from the I'm.
This is usually a Bad Idea.
Working 20% below ratings is only slightly less loud but may live a LOT longer.
This is usually a Bad Idea.
Working 20% below ratings is only slightly less loud but may live a LOT longer.
What PRR says above ^
Never push audio power chips to their limits. The voltage rating is only part of the story and you have to consider current flow into the speaker as well.
Transformer voltages are specified at full load. It will be more than that with no load. You also need to take into account that the mains voltage can be higher than nominal (by about 10%, depending on country), causing the output voltage to increase in proportion. This is especially worth remembering here in the UK where it's nominally 230V but actually 240V.
I don't see any comment about the link I posted above, according to Dimdim (and if I understood correctly, of course), we should take the rectifier diodes into account:
When working out what is safe you should take the minimum rectifier drop, not the maximum drop. So assume 1V for a bridge, not 1.8V. However, this only matters if you are near the maximum voltage, which is a bad idea anyway. So can be considered irrelevant.
Sorry, not clear for me, should we consider 1.8V max drop irrelevant, or even 1V drop irrelevant?
Thank you
W.r.t. +/- 52 Vdc, it is rather irrelevant if you really have +/- 52 or +/- 51.2 Vdc.
Best regards!
Best regards!
The higher the voltages and the less it matters in practice, particularly for non critical non regulated supplies as here. If you were working with a low voltage transformer then diode drop becomes a very important part of the calculations.
We also have losses in conductors, losses in PCB print and so on, many variables all of which tend to become less and less important when you have lots of voltage to begin with.
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